1. Field of the Invention
The present invention relates to a film molding apparatus and method, and more particularly to a film molding apparatus and method capable of molding a para orientation type aramid film at deep drawing.
The term "para orientation type aramid" herein used throughout the specification means a polymer of a repetition structure wherein a para position or equivalent position of an aromatic ring is replaced with an amido radical.
2. Description of the Related Art
The following three methods are known for deforming a thermoplastic film with metal dies and thermally setting it. The first method is a vacuum molding method. With the second method, a film is first clamped with heated metal dies and thereafter it is molded by cooling the metal dies. With the third method, a film is first heated and thereafter it is clamped and molded with low temperature metal dies.
The first vacuum molding method will be described with reference to FIG. 13.
As shown in FIG. 13(A), a film pulled out of a roll is clamped by a clamper and heated near an oven.
After the film is heated and softened, the clamper goes down to make the film in contact with a metal die, as shown in FIG. 13(B).
Next, as shown in FIG. 13(C), air is sucked via holes extending from the surface to the back of the metal die so that the film is cooled by the metal die. During the cooling operation, the oven is retracted so as not to heat the film.
After the film takes a strength retaining the shape of the metal die, the film or metal die is moved to detach the film from the metal die.
Referring to FIG. 14, there will be described the second method of clamping a film with heated metal dies and thereafter cooling the metal dies to mold the film.
As shown in FIG. 14(A), a film is pulled out of a roll and transported between metal dies. The upper and lower metal dies are pressed against heater blocks to heat the metal dies.
As shown in FIG. 14(B), the heated upper and lower metal dies go down to clamp and mold the film. Thereafter, nozzles are disposed at the back of the metal dies to cool beth the metal dies and film with air. As shown in FIG. 14(C), after the film takes a strength retaining the shape of the metal dies, the metal dies are moved to detach the film therefrom.
Referring to FIG. 15, there will be described the third method of heating a film and thereafter clamping the film with low temperature metal dies to mold the film. As shown in FIG. 15(A), an apparatus for this method has heating and pressing sections juxtaposed each other. A film pulled out of a roll is clamped with heating metal dies at the heating section so that it is heated and softened.
As shown in FIG. 15(B), the softened film is transported to the next pressing section and clamped and molded with metal dies so that the film is cooled and takes a strength retaining the shape of the metal dies.
Next, the metal dies are moved to detach the film therefrom. The film is then transported to pick up the molded portion and heat the next film portion to be molded.
The above conventional molding methods are suitable for use in molding a thermoplastic film having a low softening point and being likely to have a stable shape after cooling.
However, a para orientation type aramid has a very high glass transition point and softening point. Therefore, the above-described conventional methods cannot mold such a film at deep drawing.
The first vacuum method in particular cannot such an aramid film toward a metal die if the film is not softened sufficiently, thereby disabling to mold the film.
The second and third methods can mold such a film only at shallow drawing. If such a film is molded at deep drawing, it may sometimes be broken during pressing, or it may sometimes change with time its shape because of a residual stress at the time of molding.
With the second method in particular, the metal dies are not heated during pressing so that the temperature control during pressing is difficult. With the third method, the upstream and downstream of a pressed portion of the film may be deformed, resulting in a low manufacturing yield.